To big changes, now, in the classroom. Most states have adopted new math and literacy guidelines for students from kindergarten through 12th grade. They're called the Common Core standards, and they rewrite the rules of what students should know grade by grade.

When it comes to math, not only are the standards changing; some of the work kids will be doing, and bringing home, will actually look different. To explain, here's NPR's Cory Turner.

CORY TURNER, BYLINE: When they talk about states' old math standards, backers of the Common Core have a favorite line. They like to say the old standards were a mile wide, and an inch deep.

DOUG SOVDE: I lived the life of having to teach too much to kids in too short a period of time.

TURNER: Doug Sovde used to teach high school math in the Seattle area.

SOVDE: There was always this constant rush and, you know, they were never learning things as deeply as I wanted them to. And the Common Core state standards really focus on learning less, and learning it deeply.

TURNER: Sovde should know. He helped write the core standards, and now works for a consortium that's developing core-aligned tests. I tracked him down because I wanted a student-eye view of one change - just one change - that kids and their parents will notice because of the core.

SOVDE: Here's a problem: 96 plus 83, which I think would fall in second grade.

TURNER: Got that - 96 plus 83. But how would you write that? Well, here's the old way, using what's known as the standard algorithm.

SOVDE: We stack them, right? We say 96 on top of 83. And we add the ones column first. We say 6 plus 3 is 9. And then we add the 9 and the 8. And we know that a 9 and 8 is going to be 17, right? So we have 179.

TURNER: Again, that's the old way. Now, the core standards don't mean an end to the standard algorithm. That would be math heresy. What they do is delay it until around fourth grade. Core backers, like Doug Sovde - they say that's to be sure kids have a firm grasp on the fundamentals, like place value.

So how do you add 96 and 83 without stacking them? Well, you use a technique called regrouping. Picture this: Instead of solving the problem vertically, you lay it out horizontally and break down the two numbers by place value.

SOVDE: And they say, well, 96 is 9 tens and 6 ones, and 83 is 8 tens and 3 ones. So how many tens do you have, and how many ones do you have?

TURNER: Well, I'll finish the radio math for you. It's 17 tens, which is obviously 170, and 9 ones. Put them together; you get 179.

Now, regrouping does take a little longer than using the standard algorithm. But advocates say it forces kids to dig their hands a little deeper into the DNA of numbers. That may be, says Jonathan Goodman, a professor of mathematics at New York University. But...

JONATHAN GOODMAN: Spending an entire year doing it horizontally in order - so that you should know that when you do it vertically, you're doing the same thing, I think maybe is a little bit going too far in the other direction.

TURNER: Though Goodman's biggest worry isn't about any one change. It's about how well the core standards, taken together, stack up against overseas standards. He's compared them side by side with the standards in countries that do really well in math - Singapore, Japan, South Korea. And his verdict: Their standards are better than the Common Core.

GOODMAN: They're more clear. They're more well thought out. They're more explicit, and they're more detailed.

TURNER: They're also, in Goodman's opinion, more challenging than the core. Believe it or not, though, there is one point where Goodman and Sovde actually agree. Both say the Common Core math standards are better, and more challenging, than many of the state standards they're replacing. And that means students and parents will both be working a little harder, to make sure the math adds up.